The mind that becomes fixed and stops in one place does not function freely. Similarly, the wheels of a cart go around because they are not rigidly in place. If they were to stick tight, they would not go around. The mind is also something that does not function if it becomes attached to a single situation.
If there is some thought within the mind, though you listen to the words spoken by another, you will not really be able to hear him. This is because your mind has stopped with your own thoughts.
If your mind leans in the direction of these thoughts, though you listen, you will not hear; and though you look, you will not see. This is because there is something in your mind. What is there is thought. If you are able to remove this thing that is there, your mind will become No-Mind, it will function when needed, and it will be appropriate to its use.
The mind that thinks about removing what is within it will by the very act be occupied. If one will not think about it, the mind will remove these thoughts by itself and of itself become No-Mind.
If one always approaches his mind in this way, at a later date it will suddenly come to this condition by itself. If one tries to achieve this suddenly, it will never get there.
This translation is by William Scott Wilson. If you read Musashi then you will meet Takuan Sōhō. In the same letter Takuan talks about the Right Mind being like water and the Confused Mind being like ice.